Adding xfce4-screenshooter to baseSDK image

Pressing the "Print Screen" button in the Apertis SDK results in a message informing the use that it:

Failed to execute child process "xfce4-screenshooter" (No such file or directory)

We currently don't have this utility in the SDK image, adding it so that users can take screen prints.

Signed-off-by: Martyn Welch martyn.welch@collabora.com